Theorem wl-ifp-ncond1 38387

Description: If one case of an if- condition is false, the other automatically follows. (Contributed by Wolf Lammen, 21-Jul-2024.)

Assertion

Ref	Expression
wl-ifp-ncond1	⊢ (¬ 𝜓 → (if-(𝜑, 𝜓, 𝜒) ↔ (¬ 𝜑 ∧ 𝜒)))

Proof of Theorem wl-ifp-ncond1

Step	Hyp	Ref	Expression
1		df-ifp 1079	. 2 ⊢ (if-(𝜑, 𝜓, 𝜒) ↔ ((𝜑 ∧ 𝜓) ∨ (¬ 𝜑 ∧ 𝜒)))
2		simpr 490	. . . 4 ⊢ ((𝜑 ∧ 𝜓) → 𝜓)
3	2	con3i 155	. . 3 ⊢ (¬ 𝜓 → ¬ (𝜑 ∧ 𝜓))
4		biorf 950	. . 3 ⊢ (¬ (𝜑 ∧ 𝜓) → ((¬ 𝜑 ∧ 𝜒) ↔ ((𝜑 ∧ 𝜓) ∨ (¬ 𝜑 ∧ 𝜒))))
5	3, 4	syl 18	. 2 ⊢ (¬ 𝜓 → ((¬ 𝜑 ∧ 𝜒) ↔ ((𝜑 ∧ 𝜓) ∨ (¬ 𝜑 ∧ 𝜒))))
6	1, 5	bitr4id 293	1 ⊢ (¬ 𝜓 → (if-(𝜑, 𝜓, 𝜒) ↔ (¬ 𝜑 ∧ 𝜒)))

This proof depends on syntax axioms:  ¬ wn 3   → wi 4   ↔ wb 209   ∧ wa 401   ∨ wo 861  if-wif 1078

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This proof depends on definitions:  df-bi 210  df-an 402  df-or 862  df-ifp 1079

This theorem is used by:  wl-ifp-ncond2  38388